It is known practice to dye keratin fibers, and in particular human hair, with dye compositions containing oxidation dye precursors, which are generally known as oxidation bases, such as ortho- or para-phenylenediamines, ortho- or para-aminophenols and heterocyclic compounds. These oxidation bases are colorless or weakly colored compounds, which, when combined with oxidizing products, give rise to colored compounds via a process of oxidative condensation.
It is also known that the shades obtained with these oxidation bases can be varied by combining them with couplers or coloration modifiers, the latter agents being chosen especially from aromatic meta-diamines, meta-aminophenols, meta-diphenols and certain heterocyclic compounds such as indole compounds.
The variety of molecules used as oxidation bases and couplers allows a wide range of colors to be obtained.
This oxidation dyeing process consists in applying to keratin fibers oxidation bases or a mixture of oxidation bases and couplers with an oxidizing agent, for example aqueous hydrogen peroxide solution, leaving the mixture to act and then rinsing the fibers. The colorations resulting therefrom are permanent, strong and resistant to external agents, especially light, bad weather, washing, perspiration and rubbing. This process, which is generally performed at basic pH, makes it possible simultaneously to obtain dyeing and lightening of the fiber, which is reflected in practice by the possibility of obtaining a final coloration that is lighter than the original color. In addition, the lightening of the fiber has the advantageous effect of giving rise to a unified color in the case of gray hair, and of bringing out the color, i.e. of making it more visible, in the case of naturally pigmented hair.
It is also known practice to dye keratin fibers by direct dyeing. The process conventionally used in direct dyeing consists in applying to keratin fibers direct dyes, which are colored and coloring molecules that have affinity for the fibers, leaving the dyes to act and then rinsing the fibers.
It is known practice, for example, to use nitrobenzene, anthraquinone, nitropyridine, azo, xanthene, acridine, azine or triarylmethane direct dyes.
This results in colorations that are particularly chromatic, but are, however, temporary or semipermanent on account of the nature of the bonds between the direct dyes and the keratin fiber. These interactions are such that the dyes are easily desorbed from the surface and/or from the core of the fiber. The colorations generally show low dyeing power and poor fastness with respect to washing or perspiration. These direct dyes are also generally light-sensitive, since the resistance of the chromophore with respect to photochemical attack is low, which leads to fading of the coloration of the hair over time. In addition, the sensitivity of these dyes to light depends on their uniform distribution or their distribution as aggregates in and/or on the keratin fiber.
It is known practice to use direct dyes in combination with oxidizing agents. However, the direct dyes are generally sensitive to the action of oxidizing agents such as aqueous hydrogen peroxide solution, which generally makes them difficult to use in lightening direct dye compositions based on aqueous hydrogen peroxide solution and on a basifying agent, or in oxidation dye compositions based on oxidation dyes.
Thus, it was proposed in patent applications FR-1 584 965 and JP-062 711 435 to dye the hair with dye compositions based on nitro direct dyes and/or on azo dispersed dyes and ammoniacal hydrogen peroxide solution, by applying to the hair a mixture of said dyes and of said oxidizing agent, prepared just before use. However, the colorations obtained are found to be insufficiently fast and disappear on shampooing, leaving the lightening of the hair fiber to show through. Such a coloration becomes unattractive by changing over time.
It has also been proposed in patent applications JP-53 95693 and JP-55 022638 to dye the hair with compositions based on cationic direct dyes of oxazine type and ammoniacal hydrogen peroxide solution, by applying to the hair, in first step, ammoniacal hydrogen peroxide solution, and then, in a second step, a composition based on the oxazine direct dye. This coloration is unsatisfactory, due to the fact that it requires a process that is made too slow by the leave-in times of the two successive steps. If, moreover, an extemporaneous mixture of the oxazine direct dye with ammoniacal hydrogen peroxide solution is applied to the hair, no coloration, or at the very most a virtually nonexistent coloration, of the hair fiber is obtained.
More recently, patent application FR 2 741 798 has described dye compositions containing azo or azomethine direct dyes comprising at least one quaternized nitrogen atom, said compositions needing to be mixed extemporaneously at basic pH with an oxidizing composition. These compositions allow fast, shiny colorations with uniform glints to be obtained. However, they do not allow keratin fibers to be dyed as strongly as with oxidation dye compositions.
Moreover, patent application FR 1 353 497, which does not however concern the dyeing of keratin fibers, discloses tetraazapentamethine compounds substituted with a benzimidazole radical and with a benzimidazolium group, which are particularly suitable for dyeing fibers based on acrylic nitrile polymers or copolymers.
There is thus a real need for direct dyes that do not have the drawbacks of those of the prior art.